Lubricant compositions containing glycerol tri-esters

ABSTRACT

A lubricant composition comprising a Group I-IV or Group VI lube base stock and a glycerol tri-ester of the formula: 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2  and R 3  are independently selected from linear or branched C 4  to C 14  alkyl groups.

FIELD

The present disclosure relates to a lubricant useful in engine oils andin general lubricant applications. The present disclosure furtherrelates to a lubricant composition containing highly non-polar basestocks, that has improved solvency for polar additives.

BACKGROUND

Poly-α-olefins (PAOs) are important non-polar lube base stocks with manyexcellent lubricant properties, including high viscosity index (VI) andlow volatility and are available in a wide viscosity range, i.e., aKv₁₀₀ of about 2 to about 600 centistokes (cSt)). PAOs are disclosed aslube base stocks, for example, in U.S. Published Patent Application No.20080177121 A1.

Other important lube base stocks are those derived from one or moreGas-to-Liquids materials (GTLs) that are derived via one or moresynthesis, combination, transformation, rearrangement, and/ordegradation/deconstructive processes from gaseous carbon-containingcompounds. GTLs are disclosed as lube base stocks, for example, in U.S.Published Application No. 2007/0265178, which is incorporated herein byreference.

Other important lube base stocks are the Groups I, II, III and VI basestocks, which are discussed in “Synthetics, Mineral Oils and Bio-BasedLubricants, Chemistry and Technology” Edited by L. R. Rudnick, publishedby CRC Press, Taylor & Francis, 2006, which is incorporated herein byreference.

Base stocks of PAOs, GTLs, and Groups I-III and VI exhibit relativelylow polarity. This low polarity leads to low solubility and dispersancyfor polar additives or sludge generated in lubricants containing thesebase stocks.

To compensate for the low polarity of base stocks of PAOs, GTLs, andGroups I-III and VI, lubricant manufacturers commonly incorporate one ormore polar co-base stocks. Commonly used co-base stocks are esters oralkylated naphthalenes, which are typically present in the lube basestock at about 1 wt % to about 50 wt % based on the total weight of thebase and co-base stocks. Esters and alkylated naphthalenes aredisclosed, for example, in U.S. Pat. Nos. 6,627,779 B2 and 6,833,065 B2as well as WO 03/035585. Other co-base stocks include variousdicarboxylic acid esters, which are disclosed, for example, in U.S. Pat.Nos. 2,936,320; 3,251,771; 3,409,553; 4,464,277; and 6,667,285.

U.S. Pat. No.3,701,730 discloses extreme pressure additives forlubricant compositions which are synthetic esters, such as (a)dibrominated neopentyl glycol esters, (b) phosphate esters,polycarboxylic acids having 2-54 carbon atoms, or (d) combinations of(a), (b) and (c).

U.S. Pat. No. 4,683,069 discloses lubricating oil compositionsexhibiting improved fuel economy which contain 0.05 to 0.2 wt % of aglycerol partial ester of a C₁₆-C₁₈ fatty acid as a fuel economyadditive.

U.S. Pat. No. 5,034,144 discloses lubricating oil compositions used forfood processing machines, which exhibit highly improved oxidationstability, wear resistance and rust prevention, comprising as the baseoil a saturated fatty acid glyceride and as an essential component, afatty acid in an amount of 0.001 to 5% by weight, based on the totalcomposition.

U.S. Pat. No. 5,262,076 discloses synthetic lubricating oils having as abase oil at least one carbonic acid ester of various disclosed polyols.

U.S. Pat. No. 5,503,762 discloses base oils with high viscosity indicesand low pour points which are mixtures of a complex ester formed fromaliphatic, cycloaliphatic or aromatic dicarboxylic acids, aliphaticpolyols containing 2 to 6 hydroxyl groups and aliphatic monocarboxylicacids containing 6 to 22 carbon atoms and adipic acid esters ofunbranched aliphatic monohydric alcohols.

U.S. Pat. No. 5,538,654 discloses a food grade lubricant composition forequipment in the food service industry, comprising (A) a major amount ofa genetically modified vegetable oil and (B) a minor amount of aperformance additive.

U.S. Pat. No. 5,658,864 discloses the use of biodegradablepolyalphaolefins (“PAOs”) to treat biodegradable industrial fluids, suchas lubricants, hydraulic fluids, fuel oils, and the like, to: (a) reducetheir pour point; (b) improve their oxidation stability performance;and/or, (c) improve their hydrolytic stability performance. A preferredindustrial fluid is mixture of vegetable oil and branched alkane wherethe average molecular weight of the alkane is about 200-400, and thealkane additionally has a sufficient degree of branching to have a pourpoint of about −25° C. or lower.

U.S. Pat. No. 6,833,065 discloses methods for preparing a blended lubebase oils comprising at least one highly paraffinic Fischer-Tropsch lubebase stocks and at least one base stock composed of alkylaromatics,alkylcycloparaffins, or mixtures thereof. The use of base stockscomposed of alkylaromatics, alkylcycloparaffins, or mixtures thereofimproves the yield of lube base oils from Fischer-Tropsch facilities, aswell as provides moderate improvements in physical properties includingadditive solubility. The disclosure provides processes for obtainingsuch blended lube base oils using the products of Fischer-Tropschprocesses.

WO 97/22572 discloses a dielectric fluid or coolant comprisingrelatively pure blends of compounds selected from the group consistingof aromatic hydrocarbons, polyalphaolefins, polyol esters, glyceroltri-esters and natural vegetable oils, along with additives to improvepour point, increase stability and reduce oxidation rate.

WO 2004/108866 discloses an improved food grade lubricant comprising atleast one vegetable oil, at least one polyalphaolefin, and at least oneantioxidant.

However, despite recent advances, there remains an unmet need in the artto formulate highly non-polar lubricant base stocks with inexpensivepolar co-solvents to improve the solubility of various lube oiladditives in the non-polar base stock. Unfortunately, conventional polarco-base stocks can be quite expensive, and when present in large amountsin a lubricant formulation, can raise the cost of the overallcomposition significantly.

SUMMARY

In a first embodiment, the present disclosure is directed to a lubricantcomposition comprising a Group I-IV or poly-internal-olefin (PIO orGroup VI) lube base stock and a glycerol tri-ester of the formula:

wherein R₁, R₂ and R₃ are independently selected from linear or branchedC₄ to C₁₄ alkyl groups.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the Group I-IV or VI lube basestock is present in an amount of 50 wt % to 99 wt %.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the lube base stock is a liquidpolyalphaolefin having a Kv₁₀₀ of from greater than 3 cSt to 10,000 cSt.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein R₁, R₂ and R₃ are the same ordifferent.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein R₁, R₂ and R₃ are linear alkylgroups.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein R₁, R₂ and R₃ are branched alkylgroups.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein R₁, R₂ and R₃ are a combinationof linear and branched alkyl groups.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the glycerol tri-ester isglycerol trioctanoate.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the glycerol tri-ester isglycerol trinonanoate.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the glycerol tri-ester isglycerol tridecanoate.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the glycerol tri-ester has aKv₁₀₀ of less than 20 cSt.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the glycerol tri-ester has a VIgreater than 90.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the liquid polyalphaolefin has aKv₁₀₀ of from greater than 3 cSt to 300 cSt.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the glycerol tri-ester has apour point of less than 0° C.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, further comprising at least one additiveselected from the group consisting of detergents, dispersants,antioxidants, antiwear additives, pour point depressants, viscosityindex modifiers, friction modifiers, defoaming agents, corrosioninhibitors, wetting agents, densifiers, fluid-loss additives and rustinhibitors.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the Group I-IV or VI lube basestock is derived from a gas-to-liquid hydrocarbon material.

In another embodiment, the disclosure is directed to a lubricantcomposition as disclosed above, wherein the Group I-IV or VI lube basestock is a Group III lube base stock.

In another embodiment, the disclosure is directed to a lubricantcomposition comprising greater than 50 wt % of a metallocene-catalyzedPAO lube base stock, having a Kv₁₀₀ from 3 cSt to 300 cSt, and less than50 wt % of a glycerol tri-ester of the formula:

wherein R₁, R₂ and R₃ are independently selected from linear or branchedC₄ to C₁₄ alkyl groups.

In another embodiment, the disclosure is directed to a lubricantcomposition comprising greater than 50 wt % of a Group III lube basestock, and less than 50 wt % of a glycerol tri-ester of the formula:

wherein R₁, R₂ and R₃ are independently selected from linear or branchedC₄ to C₁₄ alkyl groups.

DETAILED DESCRIPTION

All numerical values in this disclosure are understood as being modifiedby “about” or “approximately” the indicated value, and take into accountexperimental error and variations that would be expected by a personhaving ordinary skill in the art.

Glycerol tri-esters of the formula:

wherein R₁, R₂ and R₃ are independently selected from linear or branchedC₄ to C₁₄ alkyl groups, which can be the same or different, or can becombinations of linear and branched alkyl groups, are very effective aspolar co-base lube stocks, particularly for PAO and GTL lube base stocksand can be blended therewith to obtain clear and bright liquids fromvery low to very high concentrations. The tri-esters are amorphous, havelow glass transition temperature (Tg) and are cost-competitive withother polar co-bases. The tri-esters have advantageous lubricationproperties, such as low volatility and low viscosity.

The blends of the present disclosure have a first lube base stock of oneor more glycerol tri-esters from 1 wt % to 50 wt % and a second lubebase stock selected from a Group I to Group IV or Group VI lube basestock, preferably of one or more poly-α-olefin and/or a GTL base stockat 99 wt % to 50 wt % based on the total weight of the blend. Preferredblends have 1 wt % to 50 wt % of the first base stock and 99 wt % to 50wt % of the second base stock. More preferred blends have the first basestock at 2 wt % to 25 wt % and the second base stock at 98 wt % to 75 wt%.

The glycerol tri-esters useful as co-basestocks can be selected based onphysical properties desired. Kinematic viscosity can vary from 2 cSt to20 cSt, even from 2.5 cSt to 10 cSt, and even from 3 to 7 cSt. Noackvolatility can vary from 2 wt % to 30 wt %, even from 3 wt % to 15 wt %.Glass transition temperature, Tg, can vary from 0° C. to −90° C., andeven from −10° C. to −80° C. Viscosity index, VI, can vary from 50 to300, even from 70 to 250 and even from 90 to 250. Pour points aregenerally less than 0° C., even less than −15° C., even less than −20°C., or even less than −30° C. Kinematic viscosities at 100° C. (Kv₁₀₀)and 40° C. (Kv₄₀) are measured according to ASTM method D445. Viscosityindex is measured according to ASTM method D2270. Noack volatility ismeasured according to ASTM D5800. The pour points are measured accordingto ASTM D97.

Particularly useful glycerol tri-esters are those having C₄ to C₁₄ alkylsubstituents at the ester linkages, with average carbon length of 6 to10, even between 7 to 9 carbon atoms, from a single acid or a mixture ofacids, especially the C₈ and C₉ tri-esters exhibiting a Kv₁₀₀ of lessthan 4 cSt. These glycerol tri-esters are “green” additive solubilizersbecause they do not contain N, S, or aromatic rings and because theyalso exhibit superior oxidative and cleanliness attributes.

The glycerol tri-esters can be synthesized by reacting glycerol witheither C₄ to C₁₄ alkyl acids, or with C₄ to C₁₄ alkyl acid chlorideswith average carbon length of 6 to 10, even between 7 to 9 carbon atoms,from a single acid or a mixture of acids. The esterification procedureis carried out in the presence of a catalyst. While the selection of theparticular alkyl acids or alkyl acid chlorides is not critical, it isimportant that the reactant acids or acid chlorides be fully saturatedcompounds, i.e. having no unsaturated sites within the carbon chainsthereof. We have found that glycerol tri-esters of unsaturated organicacids will tend to degrade under the high temperature conditionstypically encountered by engine lubricating oils, forming unwantedcontaminants in the lubricating oil.

The reactants may be contacted in the presence of a heterogeneous or ahomogenous acid catalyst. The acid catalyst is used to increase the rateof reaction. The amount of catalyst is not critical, but at least enoughcatalyst must be used to provide a reasonable rate of esterification.

A conventional heterogeneous esterification catalyst may be used. Onepreferred heterogeneous catalyst that may be used is a sulfonic acidcation exchange resin having a macro-reticular structure. Thesecatalysts, their properties, and method of preparation are shown in U.S.Pat. No. 3,037,052, which is incorporated herein by reference. Suchcatalysts are available commercially and are sold under the trade nameAmberlyst by Rohm & Haas of Philadelphia, Pa. Acidic zeolite catalystsmay also be used.

Alternatively, a conventional homogenous esterification acid catalystmay be utilized in the reaction. Useful catalysts include sulfuric acid,phosphoric acid, p-toluene sulfonic acid, sodium bisulfate, potassiumbisulfate, related catalysts, and the like. Other catalysts that may beused include esters of titanium or zirconium, such as tetraalkyltitanates or zirconates (e.g. tetraethyl titanate, tetraisopropyltitanate, tetrabutyl titanate, tetra-n-propyl zirconate). Also, metaloxides such as zinc oxide, alumina, and the like can be used. Apreferred homogenous catalyst is 4-toluene sulfonic acid monohydrate. Apreferred catalyst is titanium isopropoxide.

The esterification is carried out at a temperature, pressure, and for aperiod of time sufficient to affect the desired level of conversion. Thereaction temperature is usually from 25 to 300° C., even from 50 to 250°C., and even from 100 to 220° C. The reaction is carried out for a timepreferably from 1 to 48 hours, even from 2 to 36 hours, and even from 4to 24 hours. Completion of reaction may be determined by gaschromatography analysis of the product composition.

PAOs are a class of hydrocarbons that can be manufactured by thecatalytic oligomerization (polymerization to low-molecular-weightproducts) of linear α-olefin (LAO) monomers. These typically range from1-hexene to 1-tetradecene, with 1-decene being an advantageous material,although oligomeric copolymers with lower olefins such as ethylene andpropylene may also be used, including copolymers of ethylene with higherolefins as described in U.S. Pat. No. 4,956,122 and the patents referredto therein. PAO products have achieved importance in the lubricating oilmarket. Typically there are two classes of synthetic hydrocarbon fluids(SHF) produced from linear alpha-olefins, the two classes of SHF beingdenoted as PAO and HVI-PAO (high viscosity index PAO's). PAO's ofdifferent viscosity grades are typically produced using promoted BF₃ orAlCl₃ catalysts.

Specifically, PAOs may be produced by the polymerization of olefin feedin the presence of a catalyst such as AlCl₃, BF₃, or promoted AlCl₃ orBF₃. Processes for the production of PAOs are disclosed, for example, inthe following patents: U.S. Pat. Nos. 3,149,178; 3,382,291; 3,742,082;3,769,363; 3,780,128; 4,172,855 and 4,956,122, which are fullyincorporated by reference. PAOs are also discussed in the following:Will, J. G. Lubrication Fundamentals, Marcel Dekker: New York, 1980.Subsequent to polymerization, the PAO lubricant range products aretypically hydrogenated in order to reduce residual unsaturation,generally to a level of greater than 90% of hydrogenation. HVI-PAOs maybe conveniently made by the polymerization of an alpha-olefin in thepresence of a polymerization catalyst such as Friedel-Crafts catalysts.These include, for example, boron trifluoride, aluminum trichloride, orboron trifluoride, promoted with water, with alcohols such as ethanol,propanol, or butanol, with carboxylic acids, or with esters such asethyl acetate or ethyl propionate or ether such as diethyl ether, anddiisopropyl ether. (See for example, the methods disclosed by U.S. Pat.Nos. 4,149,178 and 3,382,291.) Other descriptions of PAO synthesis arefound in the following: U.S. Pat. No. 3,742,082; U.S. Pat. No.3,769,363; U.S. Pat. No. 3,876,720; U.S. Pat. No. 4,239,930; U.S. Pat.No. 4,367,352; U.S. Pat. No. 4,413,156; U.S. Pat. No. 4,434,408; U.S.Pat. No. 4,910,355; U.S. Pat. No. 4,956,122; and U.S. Pat. No.5,068,487.

Another class of HVI-PAOs may be prepared by the action of a supported,reduced chromium catalyst with an alpha-olefin monomer. Such PAOs aredescribed in U.S. Pat. No. 4,827,073; U.S. Pat. No. 4,827,064; U.S. Pat.No. 4,967,032; U.S. Pat. No. 4,926,004; and U.S. Pat. No. 4,914,254.Commercially available PAOs include SpectraSyn™ 2, 4, 5, 6, 8, 10, 40,100 and SpectraSyn Ultra™ 150, SpectraSyn Ultra™ 300, SpectraSyn Ultra™1000, etc. (ExxonMobil Chemical Company, Houston, Tex.). Also includedare PAOs prepared in the presence of an activated metallocene catalystwith a non-coordinating anion activator or a methyaluminoxane activator,and optionally in the presence of hydrogen as discussed in U.S.Published Patent Application No. 2008/0177121 or EP1910432A1, which canhave Kv₁₀₀ values from 2 cSt to as much as 10,000 cSt, even between 3cSt to 10,000 cSt, even between 3.5 cSt to 1000 cSt, or between 4 cSt to600 cSt, or between 4 cSt to 300 cSt, or between 4 cSt to 150 cSt, orbetween 4 cSt to 100 cSt, or between 20 cSt and 300 cSt.

Polyinternalolefin (PIO) or Group VI base stocks are long-chainhydrocarbons, typically a linear backbone with some branching randomlyattached; they are obtained by oligomerization of internal n-olefins.The details about these base stocks are discussed in “Synthetics,Mineral Oils and Bio-Based Lubricants, Chemistry and Technology” Editedby L. R. Rudnick, published by CRC Press, Taylor & Francis, 2006, whichis incorporated herein by reference.

Gas-to-liquid (GTL) base oils comprise base stocks obtained from GTLmaterials that are derived via one or more synthesis, combination,transformation, rearrangement, and/or degradation/deconstructiveprocesses from gaseous carbon-containing compounds. Preferably, the GTLbase stocks are derived from the Fischer-Tropsch (F-T) synthesis processwherein a synthesis gas comprising a mixture of H₂ and CO iscatalytically converted to lower boiling materials by hydroisomerisationand/or dewaxing. The process is described, for example, in U.S. Pat.Nos. 5,348,982 and 5,545,674, and examples of suitable catalysts aredescribed in U.S. Pat. No. 4,568,663, each of which is incorporatedherein by reference.

GTL base stocks are characterized typically as having Kv₁₀₀ of from 2cSt to 50 cSt, even from 3 cSt to 50 cSt, and even from 3.5 cSt to 30cSt. The GTL base stock and/or other hydrodewaxed, orhydroisomerized/catalytically (or solvent) dewaxed wax derived basestocks useful in the present disclosure have Kv₁₀₀ in the range of 3.5cSt to 7 cSt, even 4 cSt to 7 cSt, and even 4.5 cSt to 6.5 cSt, and pourpoints of −5° C. or lower, even −10° C. or lower, and even −15° C. orlower.

The GTL base stocks derived from GTL materials, especially hydrodewaxedor hydroisomerized/catalytically (or solvent) dewaxed F-T materialderived base stocks, and other such wax-derived base stocks which arebase stock components which can be used in this disclosure are alsocharacterized typically as having viscosity indices of 80 or greater,even 100 or greater, and even 120 or greater. Additionally, in certainparticular instances, the viscosity index of these base stocks may be130 or greater, even 135 or greater, and even 140 or greater. Forexample, GTL base stocks that derive from GTL materials preferably F-Tmaterials especially F-T wax generally have a viscosity index of 130 orgreater.

Examples of useful compositions of GTL base stocks are recited in U.S.Pat. Nos. 6,080,301; 6,090,989; and 6,165,949, for example, which areherein incorporated by reference.

Base stock(s), derived from waxy feeds, which are also suitable for usein this disclosure, are paraffinic fluids of lubricating viscosityderived from hydrodewaxed, or hydroisomerized/catalytically (or solvent)dewaxed waxy feedstocks of mineral oil, non-mineral oil, non-petroleum,or natural source origin, e.g., feedstocks such as one or more of gasoils, slack wax, waxy fuels hydrocracker bottoms, hydrocarbonraffinates, natural waxes, hyrocrackates, thermal crackates, foots oil,wax from coal liquefaction or from shale oil, or other suitable mineraloil, non-mineral oil, non-petroleum, or natural source derived waxymaterials, linear or branched hydrocarbyl compounds with carbon numberof 20 or greater, even 30 or greater, and mixtures of suchisomerate/isodewaxate base stocks and base oils.

Slack waxes are waxes recovered from any waxy hydrocarbon oils,including synthetic oils such as F-T waxy oil or petroleum oils bysolvent or autorefrigerative dewaxing. Solvent dewaxing employs chilledsolvent such as methyl ethyl ketone (MEK), methyl isobutyl ketone(MIBK), mixtures of MEK/MIBK, mixtures of MEK and toluene, whileautorefrigerative dewaxing employs pressurized, liquefied low boilinghydrocarbons such as propane or butane.

Slack waxes secured from synthetic waxy oils such as F-T waxy oil willusually have zero or nil sulfur and/or nitrogen containing compoundcontent. Slack waxes secured from petroleum oils, may contain sulfur andnitrogen containing compounds. Such heteroatom compounds must be removedby hydrotreating (and not hydrocracking), as for example byhydrodesulfurization (HDS) and hydrodenitrogenation (HDN) so as to avoidsubsequent poisoning/deactivation of the hydroisomerization catalyst.

Preferred base stocks or base oils derived from GTL materials and/orfrom waxy feeds are characterized as having predominantly paraffiniccompositions and are further characterized as having high saturateslevels, low-to-nil sulfur, low-to-nil nitrogen, low-to-nil aromatics,and are essentially water-white in color.

The lubricant of the present disclosure can have API Group I-III oils assecond base stocks. Useful Group I-III base stocks have a Kv₁₀₀ ofgreater than 3 cSt to 5 cSt. API Groups I, II, and III represent basestocks typically refined from crude oil and are differentiated byviscosity index (VI), saturation content, and sulfur content.

The specifications for the lube base oils are defined in the APIInterchange Guidelines (API Publication 1509) using sulfur content,saturates content, and viscosity index, as follows:

Group Sulfur (ppm) Saturates (%) Viscosity Index (VI) I >300 <90 80-120II <300 >90 80-120 III <300 >90 >120 IV All Polyalphaolefins (PAOs) VAll Stocks Not Included in Groups I-IV VI All Poly-internal-olefins(PIOs)

Manufacturing plants that make Group I base oils typically use solventsto extract the lower viscosity index (VI) components and increase the VIof the crude to the specifications desired. These solvents are typicallyphenol or furfural. Solvent extraction gives a product with less than90% saturates and more than 300 ppm sulfur. The majority of the lubeproduction in the world is in the Group I category.

Manufacturing plants that make Group II base oils typically employhydroprocessing such as hydrocracking or severe hydrotreating toincrease the VI of the crude oil to the specifications value. The use ofhydroprocessing typically increases the saturate content above 90 andreduced the sulfur below 300 ppm. Approximately 10% of the lube base oilproduction in the world is in the Group II category, and 30% of U.S.production is Group II.

Manufacturing plants that make Group III base oils typically employ waxisomerization technology to make very high VI products. Since thestarting feed is waxy vacuum gas oil (VGO) or wax which contains allsaturates and little sulfur, the Group III products have saturatecontent above 90 and sulfur content below 300 ppm.

The lubricant of the present disclosure may optionally include lube baseoil additives such as detergents, dispersants, antioxidants, antiwearadditives, pour point depressants, viscosity index modifiers, frictionmodifiers, defoaming agents, corrosion inhibitors, wetting agents,densifiers, fluid-loss additives, rust inhibitors, and the like. Theadditives are incorporated into the blend to make a finished lubricantthat has desired viscosity and physical properties. Typically, additiveswill make up 10 wt % or less of the lubricant. Typical description ofadditives used in different lubricant product formulation can be foundin “Lubricant Additives, Chemistry and Applications” Ed. L. Rudnick,published by Marcel Dekker, Inc. New York, N.Y., 2003.

The lubricant can be employed in a variety of end uses, such asautomotive crank case lubricant, automotive engine lubricants,automotive driveline lubricants, automotive gear oils, automotivetransmission lubricants, general industrial lubricants, gear andcirculation oils, hydraulic lubricants, grease, etc.

We found that glycerol tri-esters are very effective polar co-basestocks for PAO of all viscosity ranges, GTL fluids and other hydrocarbonbase stocks such as Group I-III or Group VI, and can be blended withthese non-polar base stocks to improve their polarity, solvency andunexpectedly, their low temperature properties. These blends were clearand bright liquids from very low to very high concentrations.

We have synthesized several glycerol tri-esters using glycerol (derivedfrom plant oils and a by-product in bio-diesel process) as feed andstudied their lube properties. Base stocks with wide viscosity ranges,high VI (>80) and low pour points and excellent low temperatureproperties can be prepared.

We discovered that some of the glycerol tri-esters have unique lubeproperties, such as low Kv₁₀₀ viscosity and high VI. For example, C₉tri-ester has a Kv₁₀₀ of 3.84 cSt (<4 cSt) and VI of 124. These types ofpolar base stocks are “green” additive solubilizers, since they can bederived from renewable or sustainable sources, and also have superioroxidative and cleanliness features.

Four glycerol tri-esters were synthesized by reaction of glycerol andvarious (C₆-C₁₀) acids or acid chlorides. The lube properties andproduct performance of these esters were evaluated to developstructure-property-performance knowledge for these Group V base stocks.Other compositions can be synthesized to optimize lube properties(linear vs. branched and using various carbon length acids, i.e. C₇, C₈,C₉, etc).

EXAMPLES

Kinematic viscosities (Kv), viscosity index (VI), and pour point (PP)temperature of the products were evaluated using following techniques.Kinematic viscosity was measured according to ASTM method D445.Viscosity index was measured according to ASTM method D2270. The pourpoints are measured according to ASTM D97.

Preparation of Tri-esters Using Glycerol and Acid Chlorides Example 1Synthesis of Glycerol Trioctanoate

Glycerol (1.430 g, FW. 92.09) and octanoyl chloride (7.65 g, FW. 162.7)were weighed in a 50 ml flask and cooled down in an ice bath. Pyridine(4.0 g, FW. 79.1) was slowly added drop-wise while stirring. Thereaction mixture turned slightly yellow. After 10 minutes, the mixturewas filtered to remove pyridine HCl salt that had formed in the reactionmixture. The solution was diluted with 100 ml t-butyl methyl ether andany unreacted pyridine was removed by washing with dilute HCl solution(1N, 50 ml×2). The solution was further washed with brine and dried byMgSO₄. The t-butyl methyl ether solvent was removed by rotaryevaporation. 8.6 g of a viscous, slightly yellow product was obtained.Yield: 95.5%. The product was analyzed using IR spectroscopy.

Example 2 Synthesis of Glycerol Trinonanoate

Glycerol (1.03 g, FW. 92.09) and nonanoyl chloride (5.94 g, FW. 176.7)were weighed in a 50 ml flask and cooled down in an ice bath. Pyridine(3.0 g, FW. 79.1) was slowly added drop-wise to the flask whilestirring. The reaction mixture turned slightly yellow. After 10 minutesthe mixture was filtered to remove pyridine HCl salt that had formed inthe reaction mixture. The solution was diluted with 100 ml t-butylmethyl ether and any unreacted pyridine was removed by washing withdilute HCl solution (1N, 50 ml×2). The solution was further washed withbrine and dried by MgSO₄. The t-butyl methyl ether solvent was removedby rotary evaporation. 3.85 g of a viscous, slightly yellow product wasobtained. Yield: 57%. The product was analyzed using IR spectroscopy.

Example 3 Synthesis of Glycerol Tridecanoate

Glycerol (0.953 g, FW. 92.09) and decanoyl chloride (5.933 g, FW.190.71) were weighed in a 50 ml flask and cooled down in an ice bath.Pyridine (3.0 g, FW. 79.1) was slowly added drop-wise to the flask whilestirring. The reaction mixture turned slightly yellow. After 10 minutesthe mixture was filtered to remove pyridine HCl salt that had formed inthe reaction mixture. The solution was diluted with 100 ml t-butylmethyl ether and any unreacted pyridine was removed by washing withdilute HCl solution (1N, 50 ml×2). The solution was further washed withbrine and dried by MgSO₄. The t-butyl methyl ether solvent was removedby rotary evaporation. 4.63 g of a viscous, slightly yellow product wasobtained. Yield: 68%. The product was analyzed using IR spectroscopy.

Example 4 Synthesis of C₆/C₈ Glycerol Ester

Glycerol (10 g, FW. 92.09), octanoyl chloride (35.32 g) and hexanoylchloride (14.61) were weighed in a 500 ml flask and cooled down in anice bath. Pyridine (31.6 g, FW. 79) was added slowly drop-wise to theflask while stirring. The reaction mixture turned slightly yellow. Thereaction mixture was stirred for 16 hours at room temperature. Thesolution was diluted with 200 ml t-butyl methyl ether and stirred for 18hours. The mixture was filtered to remove pyridine HCl salt that hadformed in the reaction mixture. Any unreacted pyridine was removed bywashing with dilute HCl solution (1N, 150 ml×2). The solution wasfurther washed with brine (1×150 ml) and dried by MgSO₄. The t-butylmethyl ether solvent was removed by rotary evaporation and the productwas dried at 160° C. for 3 hours. 4.63 g of a viscous, slightly yellowproduct was obtained. Yield: 68%. The product was analyzed using IRspectroscopy. The pour point of the product was −45° C.

The physical and chemical properties of these products are shown inTable 1.

TABLE 1 (lubricant properties of glycerol esters) Glycerol Kv₄₀ Kv₁₀₀Sample # Ester (cSt) (cSt) VI Example 1 C₈-Ester 13.80 3.29 108 Example2 C₉-Ester 16.72 3.84 124 Example 3 C₁₀-Ester 24.45 4.89 125 Example 4C₆/C₈ Ester 12.43 2.97 94

The viscosities of the neat glycerol esters are generally low. Forexample, the polar C₈-ester has a Kv₁₀₀ of 3.29 cSt and a high viscosityindex of 108. The C₉-ester has a Kv₁₀₀ of 3.84 cSt (<4 cSt) and a VI of124.

Preparation of Tri-esters Using Glycerol and Saturated Organic AcidsExamples 5-8 Synthesis of Glycerol Tri-esters

Glycerol tri-esters were prepared by reacting glycerol and varioussaturated organic acids (Example 4: Cekanoic C₇ acid, Example 5: LION C₇acid, Example 6: Cekanoic C₈ acid and Example 7: Cekanoic C₉ acid) inthe presence of titanium tetra-isopropoxide as the catalyst. Theseorganic acids have slight branching in their compositions. The physicaland chemical properties of these products are shown in Table 2.

TABLE 2 (lubricant properties of glycerol esters) Glycerol Kv₄₀ Kv₁₀₀Pour Point Sample # Ester (cSt) (cSt) VI (° C.) Example 5 C₇-Ester 10.132.69 102 −75 Example 6 C₇-Ester 12.97 3.08 92 −66 Example 7 C₈-Ester17.52 3.69 92 −63 Example 8 C₉-Ester 32.72 5.47 102 −45

The glycerol tri-esters showed high VI and very low pour points.

Other compositions can be synthesized to optimize lube properties(linear vs. branched) and using various carbon length acids, i.e. C₇,C8, C₉, etc. or mixed acids.

EXAMPLES OF BLENDS OF THE PRESENT DISCLOSURE

Blend properties of various hydrocarbon base stocks like PAO, Group III,and glycerol esters are shown in Table 3 below. The glycerol esters wereblended with hydrocarbon fluids in the wt % ratio of 20:80. All theblend samples were clear and bright, which suggests that these two typesof base stocks are miscible in each other. The viscosities, viscosityindex (VI), and pour point temperatures are shown in the tables. Thetest methods for Kv₁₀₀ and Kv₄₀ was ASTM D445, for viscosity index (VI)was ASTM D2270 and for pour point (PP) was ASTM D97.

TABLE 3 Blend Base Stock ratio Kv₁₀₀ Kv₄₀ PP Type (wt %) (cSt) (cSt) VI(° C.) Hydrocarbon Base Stock Data PAO-6¹ 100:0  5.50 28.50 132 −54.0PAO 150² 100:0  153.3 1675 205 −39 Group III 100:0  3.87 16.21 137 −27.0Glycerol Tri-ester Data C₈-glycerol  0:100 3.29 13.80 108 −31.0 esterC₈/C₁₀-  0:100 3.48 14.73 115 −19.0 glycerol ester C₆/C₈  0:100 2.9712.43 94 −45.0 glycerol ester Blend Data PAO-6/C₈- 80:20 5.09 25.55 130−39.0 Ester PAO150/C₈- 80:20 64.85 577 187 −36 Ester Group III/C₈- 80:203.56 14.83 124 −27 Ester PAO-6/ 80:20 5.20 26.16 132 −36 C₈/C₁₀-EsterPAO150/ 80:20 65.40 602.61 183 −21 C₈/C₁₀ Ester Group III/ 80:20 3.6715.23 130 −33 C₈/C₁₀ Ester PAO-6/ 80:20 4.85 24.83 119 −54 C₆/C₈ EsterPAO150/ 80:20 63.78 579.7 183 −42 C₆/C₈ Ester Group III/ 80:20 3.5014.65 120 −30 C₆/C₈ Ester ¹PAO-6 is low viscosity SpectraSyn ™ 6polyalpholefin (PAO) commercially available from ExxonMobil Chemical.²PAO 150 is prepared according to U.S. Published Patent Application No.2008/0177121.

The viscosity indices (VI) of the blends are high. The viscosity ofhigh-VI fluids changes less dramatically with changes in temperaturecompared with the viscosity change of low-VI fluids. A practicalconsequence of this property is that a high-VI fluid may not need aviscosity index improver (VII) in some applications. The presence of aVII is often undesirable because many tend to be unstable toward shear.Once the VII begins to break down, the fully formulated fluid goes “outof grade” (i.e., fails to retain the original viscosity grade).

All products have very low pour points. The property of low pour pointmakes the fluid very attractive in the cold-climate applications.

While the present disclosure has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the disclosure lends itself to variations notnecessarily illustrated herein. For this reason, then, reference shouldbe made solely to the appended claims for purposes of determining thetrue scope of the present disclosure.

1. A lubricant composition comprising a Group I-IV or Group VI lube basestock and a glycerol tri-ester of the formula:

wherein R₁, R₂ and R₃ are independently selected from linear or branchedC₄ to C₁₄ alkyl groups.
 2. The lubricant composition of claim 1, whereinthe Group I-IV or Group VI lube base stock is present in an amount of 50wt % to 99 wt %.
 3. The lubricant composition of claim 1, wherein thelube base stock is a liquid polyalphaolefin having a Kv₁₀₀ of fromgreater than 3 cSt to 10,000 cSt.
 4. The lubricant composition of claim1, wherein R₁, R₂ and R₃ are the same or different.
 5. The lubricantcomposition of claim 4, wherein R₁, R₂ and R₃ are linear alkyl groups.6. The lubricant composition of claim 4, wherein R₁, R₂ and R₃ arebranched alkyl groups.
 7. The lubricant composition of claim 4, whereinR₁, R₂ and R₃ are a combination of linear and branched alkyl groups. 8.The lubricant composition of claim 1, wherein the glycerol tri-ester isglycerol trioctanoate.
 9. The lubricant composition of claim 1, whereinthe glycerol tri-ester is glycerol trinonanoate.
 10. The lubricantcomposition of claim 1, wherein the glycerol tri-ester is glyceroltridecanoate.
 11. The lubricant composition of claim 1, wherein theglycerol tri-ester has a Kv₁₀₀ of less than 20 cSt.
 12. The lubricantcomposition of claim 1, wherein the glycerol tri-ester has a VI greaterthan
 90. 13. The lubricant composition of claim 3, wherein the liquidpolyalphaolefin has a Kv₁₀₀ of from greater than 3 cSt to 300 cSt. 14.The lubricant composition of claim 1, wherein the glycerol tri-ester hasa pour point of less than 0° C.
 15. The lubricant composition of claim1, further comprising at least one additive selected from the groupconsisting of detergents, dispersants, antioxidants, antiwear additives,pour point depressants, viscosity index modifiers, friction modifiers,defoaming agents, corrosion inhibitors, wetting agents, densifiers,fluid-loss additives and rust inhibitors.
 16. The lubricant compositionof claim 1, wherein the Group I-IV or Group VI lube base stock isderived from a gas-to-liquid hydrocarbon material.
 17. The lubricantcomposition of claim 1, wherein the Group I-IV or Group VI lube basestock is a Group III lube base stock.
 18. A lubricant compositioncomprising greater than 50 wt % of a metallocene-catalyzed PAO lube basestock, having a Kv₁₀₀ from 3 cSt to 300 cSt, and less than 50 wt % of aglycerol tri-ester of the formula:

wherein R₁, R₂ and R₃ are independently selected from linear or branchedC₄ to C₁₄ alkyl groups.
 19. A lubricant composition comprising greaterthan 50 wt % of a Group III lube base stock, and less than 50 wt % of aglycerol tri-ester of the formula:

wherein R₁, R₂ and R₃ are independently selected from linear or branchedC₄ to C₁₄ alkyl groups.